Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$16.97	7.426%	$18.2302	$18.23	$18.25	$18.20
Purchase #2	$128.43	11.802%	$143.5873	$143.59	$143.60	$143.60
Purchase #3	$173.25	13.436%	$196.5279	$196.53	$196.55	$196.50
Purchase #4	$151.56	5.532%	$159.9443	$159.94	$159.95	$159.90
Purchase #5	$18.49	9.200%	$20.1911	$20.19	$20.20	$20.20
Purchase #6	$210.33	4.516%	$219.8285	$219.83	$219.85	$219.80
Purchase #7	$89.57	8.677%	$97.342	$97.34	$97.35	$97.30
7 purchase totals =	$788.60		$855.6513	$855.65	$855.75	$855.50